This invention relates to the use of certain engineered copolymers for chemical mechanical polishing (CMP) of semiconductor (and similar-type) substrates and methods relating thereto.
Broadly speaking, CMP is an enabling technology for the production of semiconductor structures and is an effective method for the removal and planarization of thin films or layers on semiconductor substrates during their production. Such semiconductor substrates often contain integrated circuits, such as, multi-chip modules, capacitors and the like. During the CMP process, a slurry or substantially particle-free polishing fluid (collectively referred to herein as a polishing composition) is used along with a polishing pad. The polishing pad motion (relative to the semiconductor substrate) in combination with the polishing fluid""s chemical reaction with the substrate surface generally results in material removal from the semiconductor substrate surface.
Semiconductor substrates used to make integrated circuits typically contain three different layers: (i) a conductive metal layer; (ii) a barrier (or liner) film between the conductive metal layer and the underlying dielectric layer; and (iii) an underlying dielectric layer typically having recessed metal lines (metal interconnects) that form the circuit interconnects in the integrated circuit.
The term xe2x80x9cdishingxe2x80x9d refers to excessive (unwanted) removal of metal from the metal interconnect precursors during CMP, thereby causing unwanted cavities in the interconnect structure. Dishing is undesirable, since it negatively affects the electrical performance of the semiconductor structure (integrated circuit). Similarly, the term xe2x80x9cerosionxe2x80x9d refers to excessive removal of dielectric material surrounding metal interconnects during CMP. Erosion is undesirable, since the dielectric layer should ideally be flawless and free of cavities to ensure optimal electrical performance of the semiconductor structure (integrated circuit).
CMP is typically used to polish the semiconductor substrate to a smooth planar polished surface on which are manufactured successive layers, which themselves can be polished by CMP. Thus, excessive dishing of interconnects (recessed in the underlying dielectric layer) and erosion of the dielectric layer surrounding the interconnects in the first layer can manifest as defects in a successive layer of a multi-layered semiconductor substrate. Semiconductors having copper circuits can be particularly difficult to polish using conventional polishing compositions, polishing pads and techniques.
The use of polyacrylic acid and polymethacrylic acid for CMP of semiconductor wafers is disclosed in U.S. Pat. No. 6,117,775.
This invention is directed to the use of certain engineered copolymers for enhanced removal of metal during CMP of semiconductor substrates, and such use can also often provide suppression of dishing in metal interconnects in semiconductor substrates. The engineered copolymer molecules for use in this invention can comprise a first moiety having at least one hydrophilic functional group such as carboxyl, hydroxyl, halogen, phosphonate, phosphate, sulfonate, sulfate, nitro and the like and a second moiety which is less hydrophilic than the first moiety. The second moiety can comprise one or more hydrophobic functional groups. The first moiety of the engineered copolymer molecules of this invention will typically align or otherwise forms bonds (preferably coordinate covalent bonds) with the substrate surface. Depending upon the embodiment selected, the second moiety of the engineered copolymer molecules often provides structural rigidity to the engineered copolymer molecules and can also enable interaction of the engineered copolymer molecules with the polishing pad surface.
Thus, the methods and compositions of this invention generally enhance the removal rate of metal from a substrate surface containing metal interconnects during CMP, while also typically minimizing dishing of the metal interconnects through controlled contact-mediated reactions between the substrate surface and the polishing pad surface.
In an embodiment, this invention is directed to suppression of dishing and enhanced clearing of metal during CMP of semiconductor or similar-type substrates, particularly substrates with metal interconnects. The polishing compositions of this embodiment preferably contain engineered copolymer molecules and can be used to polish semiconductor or similar-type substrates utilizing commercially available or the like polishing pads.
The term xe2x80x9cengineeredxe2x80x9d means that the copolymers for use in the methods of this invention are derived by a judicious choice of monomers. In an embodiment, the copolymer for use in the method of this invention is engineered from monomers to contain hydrophilic functional groups that readily form strong bonds, e.g. coordinate covalent bonds, with the substrate surface. In this embodiment, the hydrophobic functional groups provide structural rigidity to the copolymer molecule and optionally also interact with the polishing pad surface through van der Waals forces or other interactions. The engineered copolymer enhances the removal rate of metal from the substrate surface during CMP, while minimizing dishing of metal interconnects through controlled contact-mediated reactions.
In an embodiment, hydrophilic functional groups are ionizable functional groups while the hydrophobic functional groups are non-ionizable functional groups. The term xe2x80x9cup toxe2x80x9d as used herein is intended to include zero as a lower limit and to further include the identified value as an upper limit (and all values in between), i.e., xe2x80x9cup to about X,xe2x80x9d means values in a continuous range including 0 up to a value which may not be precisely X but which would be deemed to be sufficiently close to X as a practical matter to those skilled in the art, depending upon the particular embodiment or end use under consideration. Additionally, all percentages are on a weight basis unless otherwise specified.
In an embodiment, the method of this invention is performed on semiconductor substrates containing metal interconnects, preferably copper interconnects, utilizing a reactive liquid comprising a blend of one or more engineered copolymers. The copolymers are preferably present up to about 1% by weight, and each copolymer is derived from a mixture of monomers having hydrophilic functional groups and relatively less hydrophilic (hydrophobic) functional groups. The reactive liquid of this embodiment may also include: (i) up to about 15% by weight of an oxidizing agent; (ii) up to about 2% by weight of a corrosion inhibitor; and (iii) up to about 3% by weight of a complexing agent.
In an embodiment, the method of this invention is performed on semiconductor substrates containing metal interconnects, preferably copper interconnects, utilizing a reactive liquid having a pH under about 5.0, preferably in a range of about 2.8 to about 4.2, more preferably in a range of about 2.8 to about 3.8. The reactive liquid can comprise a blend of one or more engineered copolymers, typically up to about 1% by weight. Each copolymer is typically derived from a mixture of monomers having hydrophilic functional groups and hydrophobic (relatively less hydrophilic) functional groups. The reactive liquid of this embodiment may also include: (i) up to about 15% by weight of an oxidizing agent; (ii) up to about 2% by weight of a corrosion inhibitor; and (iii) up to about 3% by weight of a complexing agent.
In an embodiment, the method of this invention is performed on a semiconductor substrate containing metal interconnects, preferably copper interconnects, utilizing a reactive liquid comprising: (i) up to about 1% by weight of an engineered copolymer derived from an acrylic acid monomer and methacrylic acid monomer at a mole ratio in a range of about 1:20 to about 20:1, preferably 1:1; (ii) up to about 15% by weight of an oxidizing agent; (iii) up to about 2% by weight of a corrosion inhibitor; and (iv) up to about 3% by weight of a complexing agent.
In an embodiment, the method of this invention is performed on semiconductor substrates, such as, patterned wafers with metal interconnects, preferably copper interconnects, utilizing a reactive liquid having: (i) a pH under about 5.0; (ii) up to about 11% by weight of one or more engineered copolymers, each engineered copolymer derived from a mixture of monomers having hydrophilic functional groups and hydrophobic functional groups; (iii) up to about 15% by weight of an oxidizing agent; (iv) up to about 2% by weight of an inhibitor; and (v) up to about 3.0% by weight of a complexing agent.
In an embodiment, the method of this invention is performed on semiconductor substrates such as patterned wafers with metal interconnects, preferably copper metal interconnects, utilizing an aqueous polishing composition having: (i) a pH under about 5.0, further comprising: (ii) up to about 1% by weight of a blend of one or more engineered copolymers, each engineered copolymer derived from a mixture of monomers having hydrophilic functional groups and relatively less hydrophilic (hydrophobic) functional groups; (iii) up to about 3% by weight of abrasive particles; (iv) up to about 15% by weight of an oxidizing agent; (v) up to about 2% by weight of an inhibitor; and (vi) up to about 3.0% by weight of a complexing agent.
In an embodiment, the method of this invention is performed on a semiconductor substrate containing metal interconnects, preferably copper interconnects, utilizing engineered random copolymer molecules derived from a mixture of two or more ethylenically unsaturated monomers, said mixture containing at least about 50% by weight of an unsaturated carboxylic acid monomer.
In an embodiment, the method of this invention is performed on a semiconductor substrate containing metal interconnects, preferably copper interconnects, utilizing engineered branched copolymer molecules derived from a mixture of two or more ethylenically unsaturated monomers, said mixture containing at least about 50% by weight of an unsaturated carboxylic acid monomer.
In an embodiment, the method of this invention is performed on a semiconductor substrate containing metal interconnects, preferably copper interconnects, utilizing engineered block copolymer molecules derived from a mixture of two or more ethylenically unsaturated monomers, said mixture containing at least about 50% by weight of an unsaturated carboxylic acid monomer.
In an embodiment, the method of this invention is performed on a semiconductor substrate containing metal interconnects, preferably copper interconnects, utilizing engineered alternating copolymer molecules derived from a mixture of two or more ethylenically unsaturated monomers, said mixture containing at least about 50% by weight of an unsaturated carboxylic acid monomer.
In an embodiment, the engineered copolymers can be derived from a monomer that is an unsaturated carboxylic acid monomer, such as an ethylenically unsaturated carboxylic acid monomer. xe2x80x9cUnsaturated carboxylic acid monomer,xe2x80x9d as used herein, is either an unsaturated monocarboxylic acid monomer or an unsaturated dicarboxylic acid monomer. An unsaturated monocarboxylic acid monomer, as used herein, refers to unsaturated carboxylic acid monomers containing 3 to 6 carbon atoms per molecule with a single carboxylic acid group and water-soluble salts thereof. Suitable ethylenically unsaturated monocarboxylic acid monomers are, for example, acrylic acid, oligomeric acrylic acid, methacrylic acid, crotonic acid, vinylacetic acid and derivatives thereof such as corresponding anhydrides, amides, esters and water-soluble salts thereof. An unsaturated dicarboxylic acid monomer, as used herein, refers to unsaturated dicarboxylic acid monomers containing 4 to 8 carbon atoms per molecule, anhydrides of the cis- and trans-dicarboxylic acids, and water-soluble salts thereof. Suitable unsaturated dicarboxylic acid monomers useful in the process of the present invention include, for example, maleic acid, fumaric acid, alpha-methylene glutaric acid, itaconic acid, citraconic acid, mesaconic acid, cyclohexenedicarboxylic acid, and derivatives such as corresponding anhydrides, amides, esters and water-soluble salts thereof.
In another embodiment, the engineered copolymer for use in this invention is derived from other monoethylenically unsaturated monomers such as vinylaromatic monomers that include, for example, styrene, xcex1-methylstyrene, vinyltoluene, ortho-, meta- and para-methylstyrene, ethylvinylbenzene, vinylnaphthalene and vinylxylenes. The vinylaromatic monomers can also include their corresponding substituted counterparts, for example, halogenated derivatives, that is, containing one or more halogen groups, such as fluorine, chlorine or bromine; and nitro, cyano, alkoxy, haloalkyl, carbalkoxy, carboxy, amino and alkylamino derivatives. Yet another class of suitable monoethylenically unsaturated monomers is nitrogen-containing ring compounds, for example, vinylpyridine, 2-methyl-5-vinylpyridine, 2-ethyl-5-vinylpyridine, 3-methyl-5-vinylpyridine, 2,3-dimethyl-5-vinylpyridine, 2-methyl-3-ethyl-5-vinylpyridine, methyl-substituted quinolines and isoquinolines, 1-vinylimidazole, 2-methyl-1-vinylimidazole, N-vinylcaprolactam, N-vinylbutyrolactam and N-vinylpyrrolidone. Monoethylenically unsaturated monomers also comprise ethylene and substituted ethylene monomers, for example: xcex1-olefins such as propylene, isobutylene and long chain alkyl xcex1-olefins (such as (C10-C20)alkyl xcex1-olefins); vinyl alcohol esters such as vinyl acetate and vinyl stearate; vinyl halides such as vinyl chloride, vinyl fluoride, vinyl bromide, vinylidene chloride, vinylidene fluoride and vinylidene bromide; vinyl nitriles such as acrylonitrile and methacrylonitrile.
In another embodiment, the engineered copolymer for use in this invention is derived from the polymerization of acrylic monomers and alkyl methacrylate monomers. Examples of the alkyl methacrylate monomer where the alkyl group contains from 1 to 6 carbon atoms (also called the xe2x80x9clow-cutxe2x80x9d alkyl methacrylates), are methyl methacrylate (MMA), methyl and ethyl acrylate, propyl methacrylate, butyl methacrylate (BMA) and butyl acrylate (BA), isobutyl methacrylate (IBMA), hexyl and cyclohexyl methacrylate, cyclohexyl acrylate and combinations thereof. Examples of the alkyl methacrylate monomer where the alkyl group contains from 7 to 15 carbon atoms (also called the xe2x80x9cmid-cutxe2x80x9d alkyl methacrylates), are 2-ethylhexyl acrylate (EHA), 2-ethylhexyl methacrylate, octyl methacrylate, decyl methacrylate, isodecyl methacrylate (IDMA, based on branched (C10)alkyl isomer mixture), undecyl methacrylate, dodecyl methacrylate (also known as lauryl methacrylate), tridecyl methacrylate, tetradecyl methacrylate (also known as myristyl methacrylate), pentadecyl methacrylate and combinations thereof. Also useful are: dodecyl-pentadecyl methacrylate (DPMA), a mixture of linear and branched isomers of dodecyl, tridecyl, tetradecyl and pentadecyl methacrylates; and lauryl-myristyl methacrylate (LMA), a mixture of dodecyl and tetradecyl methacrylates. Examples of alkyl methacrylate monomers where the alkyl group contains from 16 to 24 carbon atoms (also called the xe2x80x9chigh-cutxe2x80x9d alkyl methacrylates), are hexadecyl methacrylate (also known as cetyl methacrylate), heptadecyl methacrylate, octadecyl methacrylate (also known as stearyl methacrylate), nonadecyl methacrylate, eicosyl methacrylate, behenyl methacrylate and combinations thereof. Also useful are: cetyl-eicosyl methacrylate (CEMA), a mixture of hexadecyl, octadecyl, and eicosyl methacrylate; and cetyl-stearyl methacrylate (SMA), a mixture of hexadecyl and octadecyl methacrylate.
Additional examples of monomers that are used to derive the engineered copolymer for use in this invention are those alkyl methacrylate and acrylate monomers with a dialkylamino group in the alkyl radical, such as dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate; dialkylaminoalkyl methacrylamide and acrylamide monomers, such as N,N-dimethylaminoethyl methacrylamide, N,N-dimethylaminopropyl methacrylamide, N,N-dimethylaminobutyl methacryl-amide, N,N-diethylaminoethyl methacrylamide, N,N-diethylaminopropyl methacrylamide and N,N-diethylaminobutyl methacrylamide. Alkyl methacrylate and acrylate monomers with one or more hydroxyl groups in the alkyl radical, especially those where the hydroxyl group is found at the xcex2-position (2-position) in the alkyl radical. Hydroxyalkyl methacrylate and acrylate monomers in which the substituted alkyl group is a (C2-C6)alkyl, branched or unbranched, are preferred. Among the hydroxy-alkyl methacrylate and acrylate monomers suitable for use in the present invention are 2-hydroxyethyl methacrylate (HEMA), 2-hydroxyethyl acrylate, 2-hydroxypropyl methacrylate, 1-methyl-2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 1-methyl-2-hydroxyethyl acrylate, 2-hydroxybutyl methacrylate and 2-hydroxybutyl acrylate. The preferred hydroxy-alkyl methacrylate and acrylate monomers are HEMA, 1-methyl-2-hydroxyethyl methacrylate and 2-hydroxypropyl methacrylate. A mixture of the latter two monomers is commonly referred to as xe2x80x9chydroxypropyl methacrylatexe2x80x9d or HPMA, which is the more preferred hydroxyalkyl methacrylate, as are each of the components of HPMA.
Amine-containing monomers suitable for use in the present invention include, for example, amide monomers such as dialkylaminoalkyl acrylamides or methacrylamides (for example, dimethylaminopropyl methacrylamide), N,N-bis-(dimethylaminoalkyl) acrylamides or methacrylamides, N-xcex2-aminoethyl acrylamide or methacrylamide, N-(methylamino-ethyl)acrylamide or methacrylamide, aminoalkylpyrazine acrylamides or methacrylamides; acrylic ester monomers such as dialkylaminoalkyl acrylates or methacrylates (for example, dimethylaminoethyl acrylate or methacrylate), xcex2-aminoethyl acrylate or methacrylate, N-(n-butyl)-4-aminobutyl acrylate or methacrylate, methacryloxyethoxyethylamine, and acryloxypropoxypropoxypropylamine; vinyl monomers such as vinyl pyridines; aminoalkyl vinyl ethers or sulfides such as xcex2-aminoethyl vinyl ether, xcex2-aminoethyl vinyl sulfide, N-methyl-xcex2-aminoethyl vinyl ether or sulfide, N-ethyl-xcex2-aminoethyl vinyl ether or sulfide, N-butyl-xcex2-aminoethyl vinyl ether or sulfide, and N-methyl-3-aminopropyl vinyl ether or sulfide; N-acryloxyalkyloxazolidines and N-acryloxyalkyltetrahydro-1,3-oxazines such as oxazolidinylethyl methacrylate, oxazolidinylethyl acrylate, 3-(xcex3-methacryloxypropyl)tetrahydro-1,3-oxazine, 3-(xcex2-methacryloxyethyl)-2,2-pentamethylene-oxazolidine, 3-(xcex2-methacryloxyethyl)-2-methyl-2-propyl-oxazolidine, N-2-(2-acryloxyethoxy)ethyl-oxazolidine, N-2-(2-methacryloxyethoxy)-ethyl-5-methyl-oxazolidine, 3-[2-(2-methacryloxyethoxy)ethyl]-2,2-dimethyloxazolidine, N-2-(2-acryloxyethoxy)ethyl-5-methyl-oxazolidine, 3-[2-(methacryloxyethoxy)-ethyl]-2-phenyl-oxazolidine, N-2-(2-methacryloxyethoxy)ethyl-oxazolidine, and 3-[2-(2-methacryloxyethoxy)ethyl]-2,2-pentamethylene-oxazolidine.
The engineered copolymer for use in this invention can also be derived from a monomer with an unsaturated sulfonic acid monomer selected from one or more of 2-acrylamido-2-methyl-1-propanesulfonic acid, 2-methacrylamido-2-methyl-1-propanesulfonic acid, 3-methacrylamido-2-hydroxy-1-propanesulfonic acid, allylsulfonic acid, allyloxybenzenesulfonic acid, 2-hydroxy-3-(2-propenyloxy)propanesulfonic acid, 2-methyl-2-propene-1-sulfonic acid, styrene sulfonic acid, vinyl sulfonic acid, 3-sulfopropyl acrylate, 3-sulfopropyl methacrylate and water-soluble salts thereof.
Engineered copolymers derived from combinations of the aforementioned classes of monomers are used in various embodiments of this invention. Henceforth, the term xe2x80x9cengineered copolymerxe2x80x9d includes copolymers derived from polymerization of monomers selected from the aforementioned classes of monomers. The term copolymer includes the various embodiments: random copolymers, branched copolymers, block copolymers and alternating copolymers.
Material removal during CMP of semiconductor substrates is through contact-mediated reactions between the substrate surface and the polishing pad surface in the presence of a polishing composition. U.S. Pat. No. 5,489,233 teaches the importance of macro-texture and micro-texture on the polishing pad surface in controlling material removal rates during CMP and is herein incorporated by reference.
U.S. Pat. No. 5,932,486 teaches a method for polishing semiconductor substrates utilizing a reactive liquid and a polishing pad having nanoasperities (micro-texture) for CMP of semiconductor substrates. U.S. Pat. No. 5,932,486 also teaches the importance of a polishing pad having nanoasperities and chemically reactive liquid solutions to effect contact-mediated reactions and is herein incorporated by reference.
Polyacrylic acid (PAA) can be used in polishing compositions for CMP of copper substrates to lower removal of copper and lower dishing of copper in metal lines on the substrate surface. Polymethacrylic acid (PMAA), a homopolymer of methacrylic acid, when used in polishing compositions for CMP of copper substrates can be used for improved clearing of copper residuals with higher dishing of copper in metal lines on the substrate.
The copolymer for use in some embodiments of this invention can be engineered from monomers with specific hydrophilic functional groups and specific hydrophobic functional groups. In an embodiment, the engineered copolymers of this invention also have a specific rigidity by varying the mole ratio of the specific monomers. An exemplary engineered copolymer is synthesized utilizing acrylic acid monomer and methacrylic acid monomer at a mole ratio in a range of about 1:20 to about 20:1, preferably about 1:1 (xc2x125%). Where two monomers are utilized to synthesize the copolymer, the mole ratio of each monomer can be varied from about 1:20 to about 20:1. Where more than two monomers are used to generate the copolymer, the mole ratios of the various monomers can be optimized such that the total of all mole ratios is 1. In an embodiment, the engineered copolymer of this invention is generated from at least two monomers wherein one monomer is polyethylenically unsaturated and serves as the extending (crosslinking) agent in the copolymer.
Removal of material (for e.g. copper) from the substrate surface during CMP utilizing a polishing composition containing a corrosion inhibitor (for e.g. benzotriazole) and engineered copolymer molecules derived from monomers having hydrophilic functional groups and hydrophobic functional groups typically involves constant redistribution and competitive binding between the corrosion inhibitor molecules, the engineered copolymer molecules and the substrate surface. Hydrophilic functional groups of many of the above described engineered copolymer molecules can often form strong bonds, for e.g. coordinate covalent bonds, with the substrate surface. The substrate surface comprises hydrated metal atoms and hydrated metal atom-corrosion inhibitor molecular complexes. An exemplary copper substrate during CMP with the method of this invention contains hydrated copper atoms and hydrated copper atom-BTA complexes. Hydrophobic functional groups of many of the above-described engineered copolymer molecules form strong van der Waals bonds with nanoasperities on the polishing pad surface. Thus, the method of this invention when applied to substrates containing metal interconnects results in metal removal and minimal dishing of metal interconnects through controlled contact-mediated reactions.
Polishing compositions used in CMP typically contain abrasive particles that include but are not limited to alumina, silica, ceria, germania, diamond, silicon carbide, titania, zirconia and various mixtures thereof. In an embodiment, the polishing composition of this invention does not contain any abrasive particles. In another embodiment, the polishing composition contains low levels of abrasives in a range from about 0 to about 3%, with an average particle diameter less than 50 nm. In other embodiments, the weight % of abrasive can be up to about 50%.
Oxidizing agents used in polishing compositions for CMP include but are not limited to peroxides such as hydrogen peroxide, iodates such as potassium iodate, nitrates such as cesium nitrate, barium nitrate, ammonium nitrate, and/or mixtures of ammonium nitrate and cesium nitrate, carbonates such as ammonium carbonate, and persulfates such as ammonium persulfate and/or sodium persulfate and perchlorates.
Complexing agents used in polishing compositions for CMP include but are not limited to straight chain mono-and dicarboxylic acids and their corresponding salts such as malic acid and malates; tartaric acid and tartarates; gluconic acid and gluconates; citric acid and citrates; malonic acid and malonates; formic acid and formates; lactic acid and lactates; phthalic acid and phthalates. Polyhydroxybenzoic acid and its salts can also be used in the polishing composition of this invention. Complexing agents include a carboxylic acid containing two or more carboxylate groups with hydroxy groups as disclosed in Brancaleoni et al U.S. Pat. No. 5,391,258 issued Feb. 21, 1995, which is herein incorporated by reference.
Corrosion inhibitors used in polishing compositions for CMP include BTA (benzotriazole) and TTA (tolyltriazole) or mixtures thereof. Other inhibitors that are suitable for use include: 1-hydroxybenzotriazole,N-(1H-benzotriazole-1-ylmethyl)formamide; 3,5-dimethylpyrazole; indazole; 4-bromopyrazole; 3-amino-5-phenylpyrazole; 3-amino-4-pyrazolecarbonitrile; 1-methyimidazole; Indolin QTS and the like.
Polishing compositions used for CMP also contain pH buffers such as amines, and may contain surfactants, deflocculants, viscosity modifiers, wetting agents, cleaning agents and the like. The polishing composition of this invention can be used with any conventional polishing pad or non-conventional polishing pad.
The following examples illustrate various aspects of this invention. All parts and percentages are on a weight basis (i.e., by weight of the polishing composition) and all molecular weights are determined by gel permeation chromatography (GPC) and are weight-average molecular weights unless otherwise indicated.